Replaced Valve Cover Gaskets, New Coils, New Plugs....car still stumbles. What Now??

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P Rock

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Ok. I've replaced both valve cover gaskets, cleaned out all the oil in the wells, replaced ALL 8 coils, ALL 8 spark plugs. Took her for a drive today and the car still stumbles and has a rough idle. .....exactly like it did before.
There was alot of oil in the plug wells that had to be cleaned out and I knew that had to be done anyways but I'm very dissappointed the car still doesn't run right.

I do notice a gasoline smell when the car accellerates from a dead stop.

At idle, the car shakes and sounds unsteady. On the freeway under light accelleration, the car vibrates and misses around 40-60 mph (approx).

What else could it be? I feel very dejected after spending all this time and money.

ANY help would be appreciated.
 
Injector possible? Considering you've narrowed down the other possibilities. The fact that you smell gas sounds like unburned fuel, which would normally be spark. MAF sensor? Do you get a CEL?
 
I got a CEL before changing out the coils, plugs etc, but it's gone now.

Then again, I just finished all this today. I've only driven it about 20 miles since reconnecting the battery.
 
Wow, hardly singled out, thats three cylinders.

That leaves me guessing, usually one does it and gives you some direction. Its sounds more wide spread, maybe something that feeds all. MAF or maybe fuel pressure related.

Someone should be more helpful.
 
.....thanks, I'll go and clean the mass air sensor now. I also forgot to mention the fuel filter was also replaced last week by me.

Can I use brake cleaner to clean the mass air sensor connectors?
 
Ahhh, the connectors? probably, but you should probably use an electric connection type cleaner. Your MAF shouldn't be cleaned or can only be cleaned with certain things. I would hesitate to clean that stuff with brake cleaner.

You changed the fuel filter, was the problem starting then?

This has been talked about before, I hope someone can help better than me.
 
I've been searching and searching.... Injectors and mass air sensor seem to be the next logical problem(s). I want to start with the simpler one which would be the mass air sensor. I will buy electrical connection cleaner and try cleaning the sensor tomorrow.

After changing the fuel filter, nothing changed in the car's behavior.

Thanks stepping up and helping :)
 
Since you smell gas, take a good look at the FRPS and see if it's bad. Check the vacuum line for gas...or see if you can smell gas in the oil. It would also be a very good idea to get your hands on a fuel pressure gauge and watch your fuel pressures.
 
I also wanted to point out that the car was running like crap when I got emissions checked too and it passed. This may rule out the mass air sensor being dirty/faulty.
 
i would check all vacuum lines.

have you done basic checking like shaking vacuum hoses and wires while the car is running to see if the idle changes at all? Another old trick is to carefully spray carb cleaner here and there near the vacuum hoses. when the idle changes, you know you found the area.
 
I have had the same problem just once and a while notice a little cough and spitting. But can seem to find the source. Just changed my valve cover gaskets, new plugs, air filter, fuel filter, checked all my coils, even tried 94 octane gas. Set my xcal2 at 650rpm idle. Just everything and anything but still does it once and a while. Just starting to get use to it being there.
 
I had the codes pulled today and it says the miss is in cylinders 1 & 2. Thankfully, they're in the easiest cylinders to get to.

When I changed out the coils, I didn't get the rubber boots along with it (generic coils). I doubt it but could this have anything to do with it? I did notice a couple of the old boots were slightly ripped but I did a pretty good job of cleaning oil off of them and in the plug wells.
 
bad boots could DEFINITELY cause your problem. That spring that runs down through is looking for the easiest place to short to a ground and under load that path just may be your head instead of the spark plug. Replace your boots and see what happens...:)
 
beaups you are 100% correct.

I bought two boots from the lincoln dealer today ($12 a piece, yikes!!) since I remember two of them being ripped at the bottom. I replaced the boots on the cylinders the computer told me were misfiring and now it runs like new. I love my LS8 all over again :)
 
glad it worked for you:) too bad I can't solve my own problems:):)
 
....I spoke too soon. Check engine light came back on but the car IS still running like a champ. I think I have another boot that is ripped. I will pull them tomorrow.

Thanks again!
 
It doesn't take much to arc out. And the miss, well your going to feel it. Hope this finally does it for ya.

Sad part, I know whats coming

Good part, I know whats coming.

Does that make any sense?
 
I don't feel any misses anymore. Car runs as smooth as ever. I don't know why the CEL came back on but I think there's another ripped boot in there somewhere. Car does feel MUCH stronger though so i don't know if I have a miss or not. WOuld I feel it with one cylinder missing like I did when 2+ were missing?
 
I think you'll typically only feel a miss if it's "in and out". If a cylinder is dead (meaning it's never firing) then you may not feel that...just lost power.
 
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